Recently, hard disk drives are increasingly used not only for a server or computer, but also for various applications such as home hard disk recorders, car navigation systems, and portable audio-video reproducing equipment. In addition, capacity of the drive tends to increase with progress in digitalization of various applications. A hard disk as a recording medium needs an increase in recording density in order to increase capacity of the hard disk. As a technique for increasing recording density of the hard disk, patterned media is expected to be introduced in the future. A current hard disk records data by magnetizing a magnetic film formed on a surface of a disk substrate. However, bit patterned media (one example of the patterned media) is provided such that a bit pattern of a magnetic material is formed on a surface of a disk substrate, and one convex portion in the bit pattern corresponds to a unit of recording.
Japanese Patent Publication No. 2006-185545 (“Patent document 1”) describes that while discrete track, which is one of the patterned media, is used to enable high density recording, a magnetic track of a magnetic disk needs to be situated concentrically with a rotational center of a spindle motor in order to accurately perform recording and reproducing, and describes that a recognition track is formed in a landing area at an outer circumferential side of a data recording area in order to measure the amount of eccentricity of the magnetic disk with respect to the rotational center of the spindle motor.
Japanese Patent Publication No. 2006-318611 (“Patent document 2”) describes that a mirror or a transparent part for reflecting or transmitting detected light is formed in an inner or outer circumferential portion of discrete track media as a positioning mark situated on a circle concentric with a discrete groove, and the discrete track media is mounted on a turntable in such a manner that a center of the positioning mark is detected, and the detected center is aligned with a rotational center of the turntable.
The patterned media are generally prepared by using a nanoimprinting technology. That is, an irregular pattern of a mold is transferred to a magnetic layer, thereby a discrete track or a bit pattern is formed. In the case that the mold itself has a defect, or a foreign substance is adhered on the mold, a pattern to be transferred also has a defect. Therefore, before the media are completed as a magnetic disk by introducing the nanoimprinting technology, in a stage that the discrete track or the bit pattern has been formed, additional inspection is necessary on whether the discrete track or the bit pattern is appropriately formed.
As a method of inspecting a fine bit pattern in several ten nanometers, use of SEM or AFM is considered. However, according to these methods, only a limited area on the disk can be inspected from the viewpoint of securing certain throughput.
Since the bit pattern mainly has a repetitive structure, a method of using an optical scatterometry is considered as the inspection method. When a fine, repetitive structure is formed on an objective surface, reflectivity of the objective surface can be calculated by using a method such as RCWA (Rigorous coupled analysis) as one of electromagnetic wave analysis methods. The scatterometry is a method of detecting a configuration of an object by fitting reflectivity obtained by calculation to actually detected reflectivity (refer to FIG. 3). In this method, since a detection view can be made large, several tens to a few hundred micrometers, in addition, reflectivity can be detected in a short time, inspection can be performed at high speed, and the whole surface of a disk can be inspected. However, according to the method, it may be considered that even if configurations of bit patterns are differently deformed from each other, surface reflectivity is not different, and it may be considered that while a fact that an objective bit pattern has a defect can be detected, a type of the defect cannot be specified.
Thus, it may be considered that both are combined, so that an optimum inspection system can be established. That is, as shown in FIG. 5, the system is designed such that the whole surface of a disk is inspected using an optical inspection apparatus, and when a type of a defect cannot be specified, detailed inspection is performed by using SEM or AFM. By establishing such a system, the whole surface of the disk can be inspected without reducing throughput, in addition, a type of a defect can be specified.
However, a position (coordinates) of a defect on a disk surface needs to be exchanged between the optical inspection apparatus, SEM, and AFM in order to establish the inspection system as above. However, since current disk media have nothing as a coordinate reference for specifying the defect position, the coordinates cannot be exchanged between them. The reason why the disk media have nothing as the coordinate reference is because the current disk is manufactured by simply stacking magnetic films and the like, and inspection of the disk is performed mainly on the number of defects, and coordinates of the defects need not be controlled.
In the patterned media being expected to be introduced in the future, detection of a center and a direction of a disk is newly required in order to specify coordinates of a disk in a condition that information for positioning is not recorded on a magnetic recording surface.
During surface inspection in a manufacturing process of patterned media, while a center and a direction of a disk need to be detected to accurately align the disk with a stage, the direction cannot be detected in a current disk.